Investigation of Copper’s Unoccupied Bands*

DFT modeling of optical properties of materials is currently focused on time-dependent and many-body techniques, including Bethe-Salpeter equation (BSE), GW approximation, as well as Hartree-Fock based methods. We explore these methods for Cu, a relevant photocathode material, as well as a seemingly well-understood metal. In the photoexcitation view, a highly excited state may have enhanced lifetime, via quasiparticle modifications of the excited-state band structure, in particular depletion of density-of-states for nearby lower energy levels. This enhances quantum efficiency (QE) for a photoemitter. We will evaluate Cu’s virtual orbitals and the possibilities of engineering a spectral gap. A discussion of Cu as a rugged photocathode and its applications specifically in the areas of the x-ray free electron lasers will also be discussed.